The purpose of the proposed project is to determine biochemical and genetic mechanisms responsible for regulating the orderly expression of genes in fungi in response to blue light-induction. The organism to be studied is the genetically well characterized Ascomycete, Neurospora crassa. N. crassa mycelia respond to blue light by synthesizing colored carotenoid pigments. It has been shown that this process is characterized by the accumulation of messenger RNAs specific to carotenoid biosynthetic genes. In addition, two blind mutants have been isolated, having properties that suggest they represent lesions in genetic loci involved in regulating gene expression in response to blue light-induction. The currently available recombinant DNA clones, Neurospora transformation system and blind mutants will be used to identify genetic regulatory elements and to begin to determine how they function and how they are arranged into control networks. Three sets of experiments with related objectives are planned for the proposed funding period. The objectives of these experiments are 1) to determine the mechanisms controlling expression of carotenoid biosynthetic genes in response to blue light 2) to isolate and characterize genetic loci that are essential for all Neurospora blue light responses and 3) to isolate and characterize additional genetic loci having properties that indicate they are light regulatory elements. This work will provide important new information concerning the biosynthesis of the most widespread group of pigments in nature. Moreover, the proposed project will increase our knowledge of the blue light response, molecular biology, and genetics of a group of organisms including many important animal and plant pathogens and may suggest methods and approaches for controlling their spread. In addition, the results will be relevant to the broader question of how organisms coordinate the stimulus of blue light into the expression of genes contributing to events including pigment biosynthesis, cell differentiation, and reproduction.